1. Field of the Invention
The present invention relates to an in-plane switching mode liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device that is capable of preventing distortion of a horizontal electric field applied to a liquid crystal layer.
2. Discussion of the Related Art
Recently, many efforts have been made to study and develop various types of flat display panels, such as liquid crystal display devices (LCDs), plasma display panels (PDPs), field emission display devices (FEDs), and vacuum fluorescent display devices (VFDs). Some of these types of flat display panels, especially LCDs, have been applied in and incorporated into various portable electronic equipment including mobile phones, personal data assistants devices (PDAs), and notebook computers because of their high quality image, lightness, small thickness, compact size and low power consumption.
In general, a liquid crystal display device has various display modes depending on an alignment of liquid crystal molecules deposited therein. Currently, a twisted nematic (TN) mode is commonly employed because of its ease of white-black display, rapid response time and low driving voltage. In a TN mode, when voltage is applied to liquid crystal molecules of the liquid crystal display device, the liquid crystal molecules are aligned at right angles to a substrate of the liquid crystal display device. However, a viewing angle of the liquid crystal display device thus is reduced due to refractive anisotropy of the liquid crystal molecules aligned at right angles to the substrate.
In order to solve the above-mentioned viewing angle problem, various types of liquid crystal display devices having wide viewing angle characteristics, such as in plane switching (IPS) mode liquid crystal display devices, have been developed. For example, in an IPS mode liquid crystal display device, liquid crystal molecules generally are aligned in a plane by including at least a pair of electrodes arranged in parallel to each other in pixel areas and forming a horizontal electric field parallel to a substrate.
FIG. 1 is a plan view of an in-plane switching mode liquid crystal display device according to a related art. In FIG. 1, a liquid crystal display panel 1 includes a plurality of gate lines 3 arranged along one direction at a predetermined interval from each other, a plurality of data lines 4 arranged along a direction perpendicular to the gate lines 3 at a predetermined interval from each other, a plurality of pixel electrodes 7a and 7b formed within pixel areas defined by the gate and data lines 3 and 4 crossing each other, a plurality of common electrodes 5a-5c formed within the pixel areas, and a plurality of thin film transistors 10 formed within the pixel areas and switched by signals of the gate lines 3 to transfer signals of the data lines 4 to the pixel electrodes 7a and 7b. The common electrodes 5a-5c and the pixel electrodes 7a and 7b are generally formed of nontransparent metal.
In addition, each of the thin film transistors 10 includes a gate electrode 11 in which a scan signal is applied from a corresponding one of the gate lines 3, a semiconductor layer 12 formed on the gate electrode 11, and source and drain electrodes 13 and 14 formed on the semiconductor layer 12 and receiving a picture signal through a corresponding one of the data lines 4. In particular, when the scan signal is applied to the gate electrode 11, the semiconductor layer 12 becomes a channel layer. In addition, the first, second and third common electrodes 5a-5c and the first and second pixel electrodes 7a and 7b are arranged parallel to the data lines 4. Further, at the middle of each of the pixel areas, a common line 16 connects to the common electrodes 5a-5c, and a pixel electrode line 18 connects to the pixel electrodes 7a and 7b, such that the pixel electrode line 18 overlaps with the common line 16.
Further, the IPS mode liquid crystal display device includes a liquid crystal layer, such that the liquid crystal molecules deposited therein are aligned parallel to the common electrodes 5a-5c and the pixel electrodes 7a and 7b. Also, the IPS mode liquid crystal display device includes a black matrix (not shown) for preventing light leakage, and the black matrix is made of nonconductive material having nonconductive characteristics. Thus, when the thin film transistor 10 is operated to apply signals to the pixel electrodes 7a and 7b, a horizontal electric field between the common electrodes 5a-5c and the pixel electrodes 7a and 7b is generated parallel to the liquid crystal display panel 1. Accordingly, the liquid crystal molecules become perpendicularly aligned to the common electrodes 5a-5c and the pixel electrodes 7a and 7b due to the horizontal electric field, thereby preventing gray level inversion caused by the refractive anisotropy of the liquid crystal molecules aligned at right angles to the liquid crystal display panel 1.
However, when the horizontal electric field is generated between the common electrodes 5a-5c and the pixel electrodes 7a and 7b, a second electric field also could be generated between the pixel electrodes 7a and 7b, and the data lines 4, such that this second electric field distorts the horizontal electric field. In this situation, the liquid crystal molecules would not be aligned perfectly parallel to the liquid crystal display panel 1, and cross talk in the vertical direction would be generated. Therefore, the first common electrode 5a is arranged between the first pixel electrode 7a and a corresponding one of data lines 4. Also, the third common electrode 5c is arranged between the second pixel electrode 7b and another corresponding one of the data lines 4, to thereby prevent an electric field from being generated between the pixel electrodes 7a and 7b and the data lines 4. In particular, to effectively prevent an electric field from being formed between the pixel electrodes 7a and 7b and the data lines 4, the first and third common electrodes 5a and 5c have to be arranged near to the corresponding data lines 4. Thus, the total number of the common electrodes 5a-5c is greater than the total number of the pixel electrodes 7a and 7b by one. Accordingly, by arranging one more common electrode in each of the pixel areas, a region for blocking light is increased. However, such arrangement undesirably lowers an aperture ratio of the IPS mode liquid crystal display device.
Alternatively, a width of the first and third common electrodes 5a and 5c has to be increased to effectively prevent an electric field being formed between the pixel electrodes 7a and 7b and the data lines 4. Similarly, such increase of a width of the common electrodes 5a and 5b also greatly lowers an aperture ratio of the IPS mode liquid crystal display device.